A possible mechanism for high-temperature superconductivity: Application to Bi and Tl compounds

We applied our previous theory of high temperature superconductivity to Bi and Tl compounds in this paper. The theory involves the role of electron pairs in the spin singlet of species Xequal-or-greater, slanted (Bi3+ (6S2), Tl(6S2) etc.) and their virtual excited state X0 (Bi5+ (6s0), Tl3+ (6s0), etc.) in the pairing interaction of quasiholes. Bi and Tl species provide additional channels of kind (Xequal-or-greater, slanted left angle bracket X0) owing to the charge fluctuations. We treated the two states of these species like a two-level Bose system. We used the pseudospin formalism to calculate the expression for the critical temperature in this paper. We also calculated numerically the value of Tc for Bi and Tl compounds and found a good agreement between theory and experiment.

Diffusion Studies in A(3)B Compounds with A15 Structure

There is a constant effort to understand the defect structure and diffusion behavior in intermetallic compounds with the A15 structure. Diffusion of elements in intermetallic compounds depends mainly on antisites and vacancies on different sublattices. In this article, we shall discuss the diffusion of elements in A(3)B compounds with the A15 structure.

Chemical-shift of the X-ray K-absorption edge of Co in some compounds, complexes and minerals

The chemical-shift of the X-ray K-absorption edge of Co was studied in a large number of compounds, complexes (spinels) and minerals of Co in its different oxidation states having widely different crystal structures and containing different types of bonding and various types of ligands, and were reported collectively, for the first time, in a single paper. A quadratic relationship was established on the basis of least-squares regression analysis to hold between the chemical-shift and the effective charge on the absorbing atom, but the dominance of the linear term was shown. This relation was utilized in evaluating the charge on the Co-ion in a number of minerals. The effect on chemical-shift of oxidation states of the absorbing atom, of the bond length, crystal structure and higher shell atoms of the molecule, and of electronegativity, atomic number and ionic radius of the ligand was discussed.

Stability of CU(2)Ln(2)O(5) compounds - Comparison, assessment and systematics

Phase diagram studies show that at ambient pressure only one ternary oxide, Cu(2)Ln(2)O(5), is stable in the ternary systems Cu-Ln-O (Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu) at high temperatures. The crystal structure of Cu(2)Ln(2)O(5) can be described as a zig-zag arrangement of one-dimensional Cu2O5 chains parallel to-the a-axis with Ln atoms occupying distorted octahedral sites between these chains. Four sets of emf measurements on Gibbs energy of formation of Cu(2)Ln(2)O(5) (Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu; Y) from component binary oxides and one set of high-temperature solution calorimetric data on enthalpy of formation have been reported in the literature. Except for Cu2Y2O5, the measured values for the Gibbs energies of formation of all other Cu(2)Ln(2)O(5) compounds fall in a narrow band (+/-1 kJ mol(-1)) and indicate a regular increase in stability with decreasing ionic radius of the lanthanide ion. The values for the second law enthalpy of formation, derived from the temperature dependence of emf obtained in different studies, show larger differences, as high as 25 kJ mol(-1) for Cu2Tm2O5. Though associated with an uncertainty of +/-4 kJ mol(-1), the calorimetric measurements help to identify the best set of emf data. The trends in thermodynamic data correlate well with the global instability index (GII) based on the overall deviation from the valence sum rule. Low values for the index calculated from crystallographic information indicate higher stability. Higher values are indicative of the larger stress in the structure.

Synthesis of ethyl arylacetates by means of Friedel-Crafts reactions of aromatic compounds with ethyl alpha-chloro-alpha-(ethylthio)acetate catalysed by ytterbium triflate

An efficient Friedel-Crafts alkylation of aromatic compounds with ethyl alpha -chloro-alpha-(ethylthio)acetate catalysed by ytterbium triflate, followed by desulfurisation of the product provides a convenient methodology for the synthesis of ethyl arylacetates of aromatic and heteroaromatic compounds. (C) 2000 Elsevier Science Ltd. All rights reserved.

Synthesis, Structure, and Solid-State Transformation Studies of Phosphonoacetate Based Hybrid Compounds of Uranium and Thorium

Three new phosphonoacetate hybrid frameworks based on the actinide elements uranium and thorium have been synthesized. The compounds [C4N2H14][(UO2)(2)(O3PCH2COO)(2)]center dot H2O, I,[C4N2H14][(UO2)(2)(C2O4)(O3PCH2COOH)(2)], II, and Th(H2O)(2)(O3PCH2COO)(C2O4)(0.5). H2O, III, are built up from the connectivity between the metal polyhedra and the phosphonoacetate/oxalate units. Compound II has been prepared using a solvent-free approach, by a solid state reaction at 150 degrees C. It has been shown that II can also be prepared through a room temperature mechanochemical (grinding) route. The layer arrangement in III closely resembles to that observed in I. The compounds have been characterized by powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and fluorescence studies.

1,2-Shift in the anodic oxidation of aromatic compounds

The 1,2-shift observed during oxidation of organic substrates can arise by involvement of cation radicals.

Using Water as a Design Element in Crystal Engineering. Host-Guest Compounds of Hydrated 3,5-Dihydroxybenzoic Acid

Thirteen host guest compounds of 3,5-dihydroxybenzoic acid (DHBA) have been structurally characterized. Water molecules occupy the peripheries of a hexagonal void, created with DHBA molecules, and act as ``hooks'' to connect the guest molecules with the host-framework via hydrogen bonding. The ``water hook'' is an OH group acting as a donor. Consequently, the guest molecules were chosen so that they contain good hydrogen bond acceptor functionalities. A number of multicomponent hydrates were isolated with stoichiometries (DHBA)(x)(H2O). (guest),. Of these, compounds with the following as guests were obtained as crystals that were good enough for single crystal work: ethyl acetate (EtOAc), diethyl oxalate, dimethyl oxalate, di(n-propyl) oxalate, diethyl malonate, diethyl succinate, chloroacetonitrile, N,N-dimethyl formamide (DMF), acetone, dimethyl sulfoxide (DMSO), 1-propanol, and 2-butanol. From 2-butanol, a hemihydrate, (DHBA)(2)(H2O), was also obtained concomitantly. Further to guest stabilization, water acts as a good mediator of effective crystal packing and also determines the topology of the host framework. En the present series of compounds, the role of water is wide ranging, and it is not easy to classify it specifically as a host or as a guest.

Molecular orbital studies on nicotinic acid, nicotinamide and related compounds

Electronic structures of nicotinic, isonicotinic and 2-picolinic acids and their amides have been investigated, using the variable-? Pariser-Parr-Pople (PPP), iterative extended Hückel and MINDO/2 methods. In addition, PPP and MINDO/2 treatments have also been applied to 3-acetylpyridine and protonated nicotinamide. Based on these calculations, dipole moments, electronic transitions, chemical and biological activity are discussed. Comparison is made with experimental results where available.

Synthesis and characterization of Ti5Te4-type molybdenum cluster compounds, AxMo5As4(A = Cu, Al, or Ga)

A new series of molybdenum cluster compounds of the general formula AxMo5As4(A = Cu, Al, or Ga) has been synthesized. They are isostructural with the host Mo5As4(Ti5Te4-type) consisting of trans-vertex shared Mo6 octahedral chains. Investigations by X-ray photoelectron and Auger electron spectroscopies revealed a charge transfer from A to Mo5As4 in AxMo5As4. The occurrence of metallic (CuxMo5As4) and non-metallic (Al2Mo5As4 and Ga2Mo5As4) properties in this isostructural series of solids is consistent with the electronic structure of Ti5Te4-type solids involving M–M bonding in the cluster chains.

Interaction of metal ions with nucleic acids and related compounds. II. Studies on Au(III)-nucleic acid system

The nature of interaction of Au(III) with nucleic acids was studied by using methods such as uv and ir spectrophotometry, viscometry, pH titrations, and melting-temperature measurements. Au(III) is found to interact slowly with nucleic acids over a period of several hours. The uv spectra of native calf-thymus DNA 9pH 5.6 acetate buffer containing (0.01M NaCIO4) showed a shift in λ max to high wavelengths and an increase in optical density at 260 nm. There was a fourfold decrease in viscosity (expressed as ηsp/c). The reaction was faster at pH 4.0 and also with denatured DNA (pH 5.6) and whole yeast RNA (pH 5.6). The order of preference of Au(III) (as deduced from the time of completion of reaction) for the nucleic acids in RNA > denatured DNA > DNA. The reaction was found to be completely reversible with respect KCN. Infrared spectra of DNA-Au(III) complexes showed binding to both the phosphate and bases of DNA. The same conclusions were also arrived at by melting-temperature studies of Au(III)-DNA system. pH titrations showed liberation of two hydroxylions at r = 0.12 [r = moles of HAuCl4 added per mole of DNA-(P)] and one hydrogen ion at r = 0.5. The probable binding sites could be N(1)/N(7) of adenine, N(7) and/or C(6)O of guanine, N(3) of cytosine and N(3) of thymine. DNAs differing in their (G = C)-contents [Clostridium perfingens DNA(G = C, 29%), salmon sperm DNA (G + C, 42%) and Micrococcus lysodeikticus DNA(G + C, 29%), salmon sperm DNA (G = C, 72%)] behaved differently toward Au(III). The hyperchromicity observed for DNAs differing in (G + C)-content and cyanide reversal titrations indicate selectivity toward ( A + T)-rich DNA at lw values of r. Chemical analysis and job's continuous variation studies indicated the existence of possible complexes above and below r = 1. The results indicate that Au(III) ions probably bind to hte phosphate group in the initial stages of the reaction, particularly at low values of r, and participation of the base interaction also increases. Cross-linking of the two strands by Au(III) may take place, but a complete collapse of the doulbe helix is not envisaged. It is probable that tilting of the bases or rotaiton of the bases around the glucosidic bond, resulting in a significant distrotion of the double helix, might take place due to binding of Au(III) to DNA.

Protein Kinase C and Anaplastic Lymphoma Kinase Targeted Compounds

The protein kinases (PKs) belong to the largest single family of enzymes, phosphotransferases, which catalyze the phosphorylation of other enzymes and proteins and function primarily in signal transduction. Consequently, PKs regulate cell mechanisms such as growth, differentiation, and proliferation. Dysfunction of these cellular mechanisms may lead to cancer, a major predicament in health care. Even though there is a range of clinically available cancer-fighting drugs, increasing number of cancer cases and setbacks such as drug resistance, constantly keep cancer research active. At the commencement of this study an isophthalic acid derivative had been suggested to bind to the regulatory domain of protein kinase C (PKC). In order to investigate the biological effects and structure-activity relationships (SARs) of this new chemical entity, a library of compounds was synthesized. The best compounds induced apoptosis in human leukemia HL-60 cells and were not cytotoxic in Swiss 3T3 fibroblasts. In addition, the best apoptosis inducers were neither cytotoxic nor mutagenic. Furthermore, results from binding affinity assays of PKC isoforms revealed the pharmacophores of these isophthalic acid derivatives. The best inhibition constants of the tested compounds were measured to 210 nM for PKCα and to 530 nM for PKCδ. Among natural compounds targeting the regulatory domain of PKC, the target of bistramide A has been a matter of debate. It was initially found to activate PKCδ; however, actin was recently reported as the main target. In order to clarify and to further study the biological effects of bistramide A, the total syntheses of the natural compound and two isomers were performed. Biological assays of the compounds revealed accumulation of 4n polyploid cells as the primary mode of action and the compounds showed similar overall antiproliferative activities. However, each compound showed a distinct distribution of antimitotic effect presumably via actin binding, proapoptotic effect presumably via PKCδ, and pro-differentiation effect as evidenced by CD11b expression. Furthermore, it was shown that the antimitotic and proapoptotic effects of bistramide A were not secondary effects of actin binding but independent effects. The third aim in this study was to synthesize a library of a new class of urea-based type II inhibitors targeted at the kinase domain of anaplastic lymphoma kinase (ALK). The best compounds in this library showed IC50 values as low as 390 nM for ALK while the initial low cellular activities were successfully increased even by more than 70 times for NPM-ALK- positive BaF3 cells. More importantly, selective antiproliferative activity on ALK-positive cell lines was achieved; while the best compound affected the BaF3 and SU-DHL-1 cells with IC50 values of 0.5 and 0.8 μM, respectively, they were less toxic to the NPM-ALK-negative human leukemic cells U937 (IC50 = 3.2 μM) and BaF3 parental cells (IC50 = 5.4 μM). Furthermore, SAR studies of the synthesized compounds revealed functional groups and positions of the scaffold, which enhanced the enzymatic and cellular activities.

A XANES study of the K-absorption edge of copper in some of its compounds and use of the same in the determination of bond length

XANES in the K-edge of copper in the systems CuO, Cu(OH)2, La2CuO4, Cu3AsO4 and CuOHF have been investigated and transitions have been assigned to the observed structures. The measurements have been used for calculating the first coordination bond distance in the above systems. It is observed that the values so determined agree fairly well with crystallographic values.

Chemoenzymatic Synthesis of Chiral Organosulfur Compounds

This thesis is primarily concerned with the enzyme- catalysed synthesis of sulfoxides using reductase and dioxygenase enzymes. Chapter 1 provides an introduction to the topic of redox chemistry with particular emphasis on the application of reductase and dioxygenase enzymes in organosulfur chemistry. Earlier literature methods for the production of enantiopure sulfoxides are reviewed. A brief discussion of the methods used for the determination of enantiomeric excess and absolute configuration is provided. Chapter 2 contains results obtained using a range of whole-cell bacteria each using a dimethyl sulfoxide reductase enzyme. The synthesis of a series of racemic sulfoxides and the development of appropriate CSPHPLC analytical methods is discussed. Kinetic resolutions of a series of sulfoxides have been achieved. Chapter 3 contains a presentation of results using dioxygenase enzymes as biocatalysts for the asymmetric sulfoxidation of dialkyl sulfoxides including thioacetal sulfoxides. A new range of monosulfoxides, cis-dihydrodiols and cis- dihydrodiol sulfoxides have been isolated in enantiopure form. Chapter 4 is focussed on the application of chiral sulfoxides in synthesis. A new chemoenzymatic route to diol sulfoxide enantiomers and the derived enantiopure phenols and catechols is discussed. The application of chemically synthesised sulfoxide enantiomers in the production of hydroxy sulfoxides is reported. Chapter 5 provides a full experimental section where the synthesis of sulfides and racemic sulfoxides is included. The methods used in the isolation and characterisation of bioproducts from the biotransformation are discussed and full experimental details given.